1. Field of the Invention
The present invention relates generally to a method of obtaining mask data well suited for forming multiple metal-interconnection layers on a ceramics substrate, and more specifically to such a method via which the thickness of metal plated on the patterns defined by a mask is substantially made constant over an entire layer.
2. Description of the Prior Art
As is known in the art, multilayer interconnections are formed by depositing alternate layers of patterned interconnections separated by dielectric layers.
A first dielectric layer is deposited on the substrate. Then, a patterned thin metal film is formed on the first dielectric layer using a mask and evaporation techniques. Subsequently, the patterned evaporated metal film is plated. Thus, a first patterned metal-interconnection layer is completed on the first dielectric layer. These operations are reiterated until a predetermined number of metal-interconnection layers are formed on the substrate.
When the evaporated metal film patterns are plated, the thickness of metal plated on the patterns should be kept constant over the dielectric layer. However, if the surface density of the evaporated patterns differs depending on portions of the dielectric layer, it is not expected to keep the thickness of the plated metal constant over the entire surface of the dielectric layer.
In more specific terms, if the surface density of the evaporated thin metal patterns of a given portion of the dielectric layer is smaller than that of other portions, the metal film patterns within such a given portion exhibit a thin plated layer. On the contrary, if the surface density of evaporated metal patterns of the given portion of the dielectric layer is larger than that of the other portions, the metal film patterns within such a given portion are plated thickly.
In order to overcome such a difficulty, when a mask is designed for evaporating patterned thin metal film on a dielectric layer, a mask designer adds dummy patterns to a portion with a small surface density in order to average the surface density of the evaporated patterns all over the dielectric layer.
However, according to the known method, the surface density of the evaporated patterns is empirically averaged by simply adding dummy patterns or pseudo-patterns. Therefore, it is extremely difficult to precisely average the surface density of the evaporated patterns on a dielectric layer. Thus, it is no longer expected to make constant the thickness of metal plated on the evaporated metal patterns. This induces difficulties during subsequent formation of the layers. Further, each of the dummy patterns takes the form of a continuous pattern and hence is liable to undesirably transfer signal components between adjacent conductive lines adjacent a dummy pattern.